Conventionally, a diagnostic ultrasound system formed for clinics. This system comprises an ultrasonic transducer, a signal transmitting unit, a signal receiving unit and a display unit. The signal transmitting unit is generated the pulse signals and connected with the ultrasonic transducer to have the pulse signals transmitted into the ultrasound by above transducer. The signal receiving unit is connected with ultrasonic transducer for receiving echo signals varied with the ultrasonic pulse echo from the tissues. The receiving unit is adapted to process the echo signals from the ultrasonic transducer in order to generate output signals to be converted into the image of the tissues. The display unit is connected with the signal receiving unit to display the image of the tissues, on the basis of the output signals from the signal receiving unit.
An ultrasonic transducer comprises a plurality of piezoelectric transducers, and each consisting of a rectangular plate of a piezoelectric device, which were cut out (dicing process) one piezoelectric material. On the side of the piezoelectric device from which acoustic waves are transmitted, an acoustic matching layer is formed for matching acoustic impedances, and an acoustic lens is formed on the surface of the acoustic matching layer. Also, a backing material that is made of rubber or the like, being high loss coefficient (sound attenuation), is adhered to the back side of the piezoelectric device.
An example of an ultrasonic transducer (used in diagnostic ultrasound systems as described above) for transmitting and receiving ultrasound is an array-arranged transducer. The dimensions of the piezoelectric device generally used in the array-arranged transducer are width W, thickness T, and length L. The piezoelectric device used in the array-arranged transducer has electrodes (a ground electrode and a signal electrode) arranged on the upper and lower surfaces. Each electrode area is multiply width W by length L.
When the pulse signal voltage is applied to the above electrodes, longitudinal vibrations in accordance with the thickness T are caused as the principal vibrations, and the lateral vibrations (lengthwise vibrations) in accordance with the width W are also caused as the subsidiary vibrations. In other words, the power of lateral vibrations become strong, when the width W is almost equal to thickness T, and these lateral vibrations may sometimes be superposed on the longitudinal vibrations depending on the shape of the piezoelectric device, such that the longitudinal vibrations are affected. Accordingly, piezoelectric device divided it into two or three pieces in such a manner that each piezoelectric device does not have one proper resonant frequency in the lateral direction.
Here, explanations are given for the steps of manufacturing an ultrasonic transducer; these steps are generally employed in order to configure the piezoelectric device in such a manner that the piezoelectric device does not have a proper resonant frequency (see Patent Document 1, for example)    (1) A backing layer is formed into the decided shape. (backing material forming step)    (2) Lead wires in the form of an FPC (Flexible Printed Circuit) board or the like are connected to electrodes that are formed on the piezoelectric device in a prescribed shape, before or after the backing material forming step. (wiring step).    (3) The first stacked body is formed by mounting the piezoelectric device and the backing layer. (piezoelectric transducer mounting step)    (4) A transducer unit serving as the second stacked body is formed by mounting the first acoustic matching layer to the piezoelectric device included in the first stacked body. (first matching layer mounting step)    (5) Dicing grooves are formed on the transducer unit from the side of the first acoustic matching layer, such that the piezoelectric device is divided into a plurality of transducer elements. (dicing step)    (6) The dicing grooves are filled with resin with particles for reinforcement. (filling step)    (7) The third stacked body is formed by mounting the second acoustic matching layer to the first acoustic matching layer. (second acoustic matching layer mounting step)    (8) An acoustic lens is cast on the third stacked body. (lens casting step)    (9) The third stacked body, including the acoustic lens, is encased. (packaging step)
Ultrasonic transducers are manufactured using the above steps in the conventional process.
Electronically scanning ultrasonic transducer is formed at the distal end of endoscope insertion tube. The ultrasonic transducer on the endoscope is transmitted the ultrasounds in the digestive tract, so this transducer can be received the ultrasounds from the digestive organ such as the stomach, the pancreas, the liver without interfered with the gas or bone. In the electronically scanning ultrasonic transducer, tens or more piezoelectric transducers are arrayed.
FIG. 1 shows a conception of piezoelectric transducers.
As shown in FIG. 1, a piezoelectric transducer 2101 is generally a rectangular shape (hexahedron) whose width is W, thickness is T, and length is L. When a voltage is applied to electrodes (not shown) on the upper and lower surfaces (thickness direction) of the rectangular shape (hexahedron) shown in FIG. 1, the rectangular shape (hexahedron) vibrates in the thickness direction and generates ultrasounds.
It has been disclosed that ultrasonic transducers such as the one described above are very efficient in the coefficient of electromechanical coupling when the W/T ratio of their piezoelectric transducer is equal to or lower than 0.8, and that the smaller the interval “a” between adjacent piezoelectric transducers, the higher the image quality (Patent Document 2 for example). Accordingly, ultrasonic transducers have conventionally been designed in such a manner that the interval “a” between adjacent piezoelectric transducers is as small as possible, and the W/T ratio is equal to or lower than 0.8.
FIG. 2 is a perspective view showing a first example of a conventional ultrasonic transducer. FIG. 3 is a cross-sectional view of the first example of the conventional ultrasonic transducer.
In FIGS. 2 and 3, the ultrasonic transducer comprises piezoelectric transducers 2123 that formed electrode layers on the upper and lower surfaces thereof, acoustic matching layers 2124 (first acoustic matching layer 2124a and second acoustic matching layer 2124b) formed under the piezoelectric transducer 2123, a GND conduction unit 2125 for connecting to GND the electrodes formed under the piezoelectric transducer 2123, dicing grooves 2126 formed by using a dicing saw (a precision cutting machine) or the like for dividing the piezoelectric transducer 2123 into plural pieces, lead wires 2131 connected to the electrodes on the lower surface of the piezoelectric transducer 2123, and a backing material 2130. In this configuration, an acoustic matching layer and piezoelectric transducers or the like having dicing grooves 2126 between them is referred to in whole as an ultrasonic transducer element.
FIG. 4 is a perspective view showing a second example of a conventional ultrasonic transducer. FIG. 5 is a cross-sectional view of the second example of the conventional ultrasonic transducer.
The transducer shown in FIGS. 4 and 5 is different from that shown in FIGS. 2 and 3 in that one lead wire 2131 is connected to two piezoelectric transducers 2123 (2123a and 2123b) and two acoustic matching layers 2124 (2124a and 2124b), and one transducer element consists of a plurality (two in FIG. 5) of transducer sub elements. By employing the configuration of sub elements as described above, it is possible to improve the ultrasonic transmission/reception characteristics (sensitivity, for example) of the ultrasonic transducer.
Here, a method of designing a conventional ultrasonic transducer is described.    (1) The effective width S of the emitting window of an ultrasonic transducer is determined on the basis of the size So of the object that is to be observed by the ultrasonic transducer in such a manner that So<S.    (2) The arraying pitch p in the ultrasonic transducer is calculated S/N: where N is the maximum number of driving channels of diagnostic ultrasound system, S is the effective width.    (3) The element number n of piezoelectric transducers with a W/T ratio of 0.8 or lower that can be included in the arraying pitch p is calculated. In the example of FIGS. 2 and 3, the number of transducer elements is n, and in the example of FIGS. 4 and 5, the number of sub elements is 2n.
In the conventional methods, configurations are employed in which a plurality of piezoelectric elements are formed such that an effective W/T ratio is achieved, as described above. Also, in some cases, fine modification has been performed on the effective width S, such that the effective W/T ratio is achieved.
The electronically scanning ultrasonic transducer is formed at the insertion tube of an endoscope. The ultrasonic transducer on the endoscope is transmitted the ultrasounds in the digestive tract, so this transducer can be received the ultrasounds from the digestive organ such as the stomach, the pancreas, the liver without interfered with the gas or bone. Examples of types of such electronically scanning ultrasonic transducers applied to the endoscopes include the convex type, the linear type, the radial type and the like.
The ultrasonic transducers generally employ the configuration in which a plurality of ultrasonic transducer elements are arrayed for transmitting and receiving the ultrasound, and only the grooves formed at the both side of each element (slots between adjacent transducer elements) are filled with resin (see Patent Document 3 for example).
Also, a method is disclosed in which adhesive is applied to several locations, including the centers of the grooves (see Patent Document 4 for example).    Patent Document 1    Japanese Patent Application Publication No. 2001-46368    Patent Document 2    Japanese Patent No. 56-17026    Patent Document 3    Japanese Patent Application Publication No. 8-107598    Patent Document 4    Japanese Patent Application Publication No. 2000-253496